An integrated circuit protection unit is defined as a circuit breaker that includes optional accessory protection features. One such integrated circuit protection unit is described in U.S. Pat. No. 4,754,247 which Patent is incorporated herein for reference purposes. The Patent includes an accessory cover which is accessible for field-installation of selected accessory functions. The circuit breaker also includes an electronic trip unit in the form of a printed wire board positioned within a recess formed in the circuit breaker cover.
A current limiting circuit breaker utilizes the electromagnetic repulsion that occurs between the fixed and movable contact arms upon intense short circuit conditions to separate the circuit breaker contacts before the circuit breaker operating mechanism has time to respond. One example of a current limiting circuit breaker is described within U.S. Pat. No. 4,375,021 which Patent is incorporated herein for reference purposes. The arrangement of the slot motor to accelerate the movement of the movable contact arm allows the circuit to be interrupted in the early stages of the current wave form and hence limits the current to a reasonable value. The specially-designed arc chute in the aforementioned Patent rapidly quenches and extinguishes the arc that occurs during the rapid separation of the contacts. The complex design of both the slot motor and arc chute, however, do not readily allow for application within an automated circuit breaker assembly process.
An effective slot motor configuration for current limiting circuit breakers is described within U.S. Pat. No. 4,220,934 wherein the slot motor comprises a stack of U-shaped laminations of magnetic material fitted within a formed housing. The U-shaped laminations define a closed-ended and open-ended slot motor wherein the movable contact arm is driven toward the open end of the slot.
A further slot motor configuration is described within U.S. Pat. No. 4,470,027 wherein a plurality of U-shaped laminations are arranged on both the top and bottom portions of a support housing to form a so-called "closed" slot motor wherein the movable contact arm moves from the bottom closed end to the top closed end of the slot.
U.S. Pat. No. 4,733,032 describes an electric arc chute wherein the configuration of the arc plates and the composition of the arc chute support material are optimized to rapidly cool and extinguish the arc that occurs upon current limiting circuit interruption. This Patent is incorporated herein for reference purposes and should be reviewed for its description of the arc quenching properties of the specific plastic resin material used within the arc chute support.
When current limiting is attempted in certain lower-rated industrial molded case circuit breakers, problems occur due to the compact size limitations on the circuit breaker components and the circuit breaker enclosure, per se. It is difficult to contain the intense arc that is generated during the current limiting circuit interruption within the compact confines of the circuit breaker enclosure without causing damage to the enclosure. It is also difficult to quench and cool the arc because of the size restraints on the circuit breaker components within the enclosure since larger arc chute designs do not readily fit within the confines of the compact circuit breaker enclosure.
One purpose of the instant invention is to provide a compact circuit breaker having a slot motor configuration that is arranged within a compact circuit breaker enclosure for rapidly driving the movable contact arm to an open position upon severe overcurrent conditions without damaging the enclosure and is readily assembled by automated means. A further purpose of the invention is to provide an efficient arc chute arrangement that rapidly quenches the arc that occurs upon separation of the circuit breaker contacts and safely directs the resulting arc gases out of the circuit breaker enclosure.